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An interferometric measurement system for small elongation

Thomas Baumgartner

The interferometric measurement system is used to measure strain in the region of some nm. Therefore two indentions are placed in polished surface of a specimen with a Vickers-Diamond. These indentions are shaped like pyramids with side lengths of ca. 20 µm and the space between them is about 100 µm. When they are illuminated by a laser they generate interference fringes which shift in phase when the distance between the two indentions changes.

A camera, a Sony XC-77CE is used in this diploma project, records the interference fringes and transmit them to a computer. The analysis takes place on the PC and tries to resolve to sub-pixel-accuracy.

The following image shows the measurement system mounted on an optical table and the fixed specimen on a bracket.

Figure 1: The measurement system

The entire measurement system is composed of three components. The optical part is shown in the image. It serves to generate the interference fringes and projects them onto the camera chip. The second part is the electronic circuit which is needed to control and for the safety of the measurement system. Therefore an Atmega8 microcontroller is integrated. The third part is a graphical user interface (GUI) which is programmed in MatLab and is used to operate the measurement system.

Keywords: interference, elongation, strain, phaseshift, interference pattern

March 12, 2013